In the bleak end-of-winter days of March 2013, I found myself reporting a story from a barge on the Mississippi River. The barge was parked near President’s Island, a forlorn peninsula in southwest Memphis blighted by chemical plants and agribusiness operations, where great drifts of garbage accumulate after heavy rains. As we bumped along over the filthy water in a speedboat, my guide pointed out an oil refinery here, a cement factory there, a Cargill corn processing facility on that bank, a coal-fired power plant on another. I noticed that my lungs had begun to burn. The air, which smelled of acrid chemicals and fermented cereal grains, was a toxic soup the likes of which I had never encountered or inhaled. But I wasn’t going to be a baby, so I ignored the searing sensation in my chest. And then, adding insult to injury, a passenger with a respiratory flu joined our group. Armed with my personal travel apothecary, I held out admirably while the hale, ruddy barge people dropped like …